As is known to those skilled in the art, there are two well-known methods of thermal printing: thermal transfer printing, and direct thermal printing. Although the thermal printing assembly of this invention is applicable to both such methods, for the sake of simplicity of discussion most of this specification will be devoted to describing the use of such assembly in thermal transfer printing.
Thermal transfer printers are well known to those skilled in the art and are described, e.g., in International Publication No. WO9700781 (Method of Making a Decal) published on Jan. 9, 1997, the entire disclosure of which is hereby incorporated by reference into this specification. As is disclosed in this publication, a thermal transfer printer is a machine that creates an image by melting ink from a film ribbon and transferring it at selective locations onto a receiving material. Such a printer normally comprises a print head including a plurality of heating elements that may be arranged in a line. The heating elements can be operated selectively.
Alternatively, one may use one or more of the thermal transfer printers disclosed in U.S. Pat. Nos. 6,124,944; 6,118,467; 6,116,709; 6,103,389; 6,102,534; 6,084,623; 6,083,872; 6,082,912; 6,078,346; and the like. The disclosure of each of these patents is hereby incorporated by reference into this specification.
It is well known that print heads in thermal transfer printers become fouled with usage; see, for example, U.S. Pat. No. 5,688,060. The operation of such print heads involves the resistive heating of selected print head elements to temperatures above 200 degrees Celsius in order to facilitate the thermal transfer of an imaging ink from a donor ribbon to a receiving sheet. As the donor ribbon is transported across the print head during the imaging process, selected areas of the ribbon are in turn heated by the energized print head elements. With usage, a build up of contaminates accumulates on the print head. Some of these contaminates may be from the ribbon itself.
Some thermal transfer printers have automatic print head cleaning devices integrated into them; see for example such U.S. Pat. No. 5,688,060 of Terao. In this patent it is disclosed that in “a thermal transfer printer in which when a printing head is soiled, the debris on the printing head can be removed automatically. The printing head movable to and from a platen is mounted on a carriage capable of being reciprocated along the platen, and a cleaning pad is disposed on an extension line of the platen downstream or upstream in the printing column direction of the platen” (see column 2). Such cleaning pads typically are saturated with solvents such as isopropyl alcohol and need to be frequently replenished.
Other print head cleaning systems utilize pouches of organic solvent integrated into the thermal transfer media. See, for example, U.S. Pat. No. 5,875,719 of Francis in which is disclosed a “cleaning apparatus for cleaning the print head of a baggage tag printer used for printing passenger identification and destination indicia thereon. The print head cleaner comprises a plurality of baggage tags secured to one another in end-to-end relation forming an elongated strip of baggage tags. The cleaner is secured to the last of the tags for automatic advancement into the printer upon completion of the printing of the final tag. The cleaner includes a quantity of print head cleaning fluid enclosed in a pouch which bursts upon passage through the printer. A paper tail may be fastened to the pouch for frictional engagement with the print head facilitating the cleaning thereof” (see columns 2 and 3 of such patent). Such systems are complex to manufacture. Thermal media is typically prepared by spooling the media onto a cylindrical core. If the cleaning pouch is placed at the end of the media, directly adjacent to the core, then it will be subjected to relatively high winding pressures, thereby placing it at risk of busting before usage. If the cleaning pouch is placed at the start of the media, then there is a danger that the cleaning solvent will spread onto the thermal media and damage it prior to use of the media. In addition, such cleaning pouches are designed to burst and, thus, may be easily broken before usage, potentially damaging the thermal media before its usage.
Methods for cleaning print heads are also discussed in U.S. Pat. No. 5,525,417 of Eyler, the entire disclosure of which is hereby incorporated by reference into this specification. According to this Eyler patent, “one conventional method for cleaning the heads, sensors, and/or rollers is to use a cleaning card. The cleaning card has the approximate dimensions of the data-carrying card. Typically, cleaning cards are constructed as a laminate of a semi-rigid core of acrylic, PVC, PET, or ABS plastic material or the like, with non-woven fibers of a soft substantially nonabrasive material chemically bonded to both of the side surfaces thereof. The cleaning card may be pre-saturated with a solvent or the solvent may be added just prior to use of the cleaning card. Unfortunately, the chemical bonding process includes binders, adhesives, and other materials which are necessary for the lamination process, but which, in the presence of the solvents required for cleaning, will deteriorate and thus undermine the structural integrity of the card. A non-laminated cleaning card has been described in U.S. Pat. No. 5,227,226 to Rzasa. The non-laminated cleaning card is porous allowing penetration of the cleaning solvent. If the equipment is exposed to such cleaning solvent for too long a period of time, the equipment may be deleteriously affected. Moreover, conventional cleaning cards often disadvantageously introduce static into the equipment” (see columns 1 and 2 of such patent).
In U.S. Pat. No. 5,525,417, Eyler disclosed a two part cleaning card for removing contamination from print heads and other devices. “The cleaning card comprises, generally, a flat, semi-rigid base with a first material mechanically bonded to a first side surface and a second material mechanically bonded to a second side surface thereof. The mechanical bonding process is also claimed. In a preferred form of the invention, the cleaning card provides a way to make the cleaning of equipment quicker and effective for removing stubborn contaminates. The base includes a flat, semi-rigid generally rectangular piece of acrylic, PVC, PET, or ABS or the like plastic material. The base is generally sized to conform to the same dimensions of the card, which carries the data and may be colored to increase its opacity and thus its ability to be accepted into some equipment. In a first preferred embodiment, the first material mechanically bonded to a first side surface is substantially abrasive. One example is Reemay® from Reemay, a non-woven spunbonded polyester. This material is substantially impenetrable to restrict absorption of a cleaning solvent. The second material mechanically bonded to a second surface comprises a spunlaced, non-woven fabric such as DuPont's Sontara® which is soft, substantially nonabrasive, lightweight, and drapable. This material is substantially penetrable to improve absorption of the cleaning solvent. In an alternative embodiment, the abrasive first material is 3M Imperial Lapping Film, also a substantially impenetrable material” (see columns 2 and 3 of such patent).
U.S. Pat. No. 5,525,417 also discloses that “Another conventional method is to remove the contaminants by wiping the surface of the heads and rollers with a soft paper or rag impregnated with a cleaning solvent. In this case, however, it is necessary to disassemble the equipment for exposing the rollers and heads” (see column 2 of such patent).
Such abrasive cleaning cards, as described, e.g., in U.S. Pat. No. 5,525,417, often damage the print head by scratching the elements of the print head during the process of abrading away debris or contamination on the print head. In addition, if it is necessary to use solvents in the cleaning of the print head, the process will be both inconvenient and potentially dangerous. Due to the flammable nature of many solvents and the static which may be generated when handling thermal media, the potential for fire or explosions is real. Many other patents disclose the use of abrasive substrates or solvents to clean various types of print heads. See, for example, U.S. Pat. Nos. 5,563,646; 5,536,328; 4,933,015; 5,926,197; 6,210,490; 5,227,226 and 6,028,614; the disclosure of each of these patents is hereby incorporated by reference into this specification.
Print head cleaning cards, such as the Sato Thermal Printer Cleaning Sheet available from Sato America, 10350A Nations Ford Road, Charlotte, N.C. 28273, are based on abrasive lapping films. These cleaning cards are comprised of a film with at lease one rough abrasive surface. The abrasive particles on this surface are strongly bound to the surface. These films typically have a Sheffield smoothness greater than 60.
According to Shinji Imai, in his U.S. Pat. No. 5,995,126, “The lapping film has an abrasive such as alumina particles buried in the surface of a substrate film and the deposits adhering tenaciously to the surface of the thermal head can be scraped off by delivering this lapping film in place of the thermal material. However, the abrasive effect of the lapping film is so great as to remove the protective ceramic coating on the thermal head and, hence, the thermal head will wear prematurely before the end of its expected service life” (see column 1 of such patent).
It is an object of this invention to provide a thermal printing and cleaning assembly that is not comprised of liquid and that effectively cleans print heads without damaging them.